The present invention relates to a sampled-data I-PD control apparatus.
An example of a sampled-value control system for controlling a multi-input/multi-output process is proposed by the present inventors as per "Design of Sampled-Data Noninterference I-PD Control System having Different Sampling Periods" (the 25th Automatic Control Association Meeting, Nov. 18 to 20, 1982). According to this system, an optimal sampling period is preset for every control loop in accordance with the characteristics and specifications of input/output loops of a process to be controlled. Therefore, unlike conventional control systems wherein the shortest sampling periods must be preset for all control loops, the calculation time for sampled-data control can be shortened. However, the design described above is based upon an assumption that the dynamic characteristic of the process is known. An auto-tuning function is not included in the above-mentioned design. In auto tuning, the process dynamic characteristic is identified during the closed loop control of the process and the sampled-data I-PD control parameters are tuned in accordance with the identification result. For this reason, when the dynamic characteristic of the process changes, the control apparatus cannot continue to control the process properly. In addition to this disadvantage, the above-mentioned design is made only to satisfy a predetermined design specification, and fails to provide flexibility in the control system. For example, in the control system, noninterfered control loops have zero steady-state errors and an overshoot of the step response by 10%. For this reason, the design specification for providing a control system which is free from overshoot cannot be obtained.